Drinking water

Water purification, or drinking water treatment, is the process of removing contaminants from surface water or groundwater to make it safe and palatable for human consumption. A wide variety of technologies may be used, depending on the raw water source, contaminants present, standards to be met, and available finances.

Sources of Drinking Water

Water to be used in public or private water supplies can be drawn from a variety of sources. Different sources of raw water demand different treatment methods to render it fit for human consumption.

Deep Groundwater - The water emerging from some deep groundwaters may have fallen as rain many decades or even hundreds of years ago. Soil and rock layers will have naturally filtered the groundwater to a high degree of clarity even before it is pumped to the treatment plant. Such water may emerge as springs, artesian springs, or may be extracted from boreholes or wells. Deep groundwater is generally of very high bacteriological quality but may be rich in dissolved solids especially carbonates and sulphates of calcium and magnesium. Depending on the strata through which the water has flowed, other ions may also be present including chloride, and bi-carbonate and there may be a requirement to reduce the iron or manganese content of this water to make it pleasant for drinking, cooking, and laundry use. Disinfection is also required. Where groundwater recharge is practised, such groundwaters should be graded as being equivalent to lowland surface waters for treatment purposes.
Shallow groundwaters - water emerging from shallow groundwaters are usually abstracted from wells or boreholes and the bacteriological quality can be variable depending on the nature of the catchment. A variety of soluble materials may be present including potentially toxic metals such as copper or zinc. In parts of Bangladesh, many shallow ground water sources are contaminated with unacceptably high levels of arsenic.
Upland lakes and reservoirs - typically located in the headwaters of rivers systems, upland reservoirs are usually sited above any human habitation and may be surrounded by some form of protection zone to restrict the opportunities for contamination. Bacteria and pathogen levels are usually low but some bacteria, protozoa and algae will be present. Where upland are forested or are peaty, humic acids can colour the water brown. Many upland sources have low pH which requires adjustment before the water is put into supply.
Rivers , Canals and low-land reservoirs - lowland surface waters will have a significant bacterial load and may also contain algae, suspended solids and a variety of dissolved constituents